1. Field of the Invention
This invention relates to syringes and more particularly to syringes with a finger flange attached to a barrel.
2. Description of Related Information
Generally speaking, a hypodermic syringe consists of a cylindrical barrel, most commonly made of a thermoplastic material or glass, having a distal end connected to a sharp needle or adapted to be connected to a hypodermic needle assembly, a proximal open end having an external finger flange and internally adapted to receive a resilient stopper.
In most cases, the finger flange is integrally formed with the barrel. The process of integrally forming the flange and the barrel limits the design of the flange, particularly in the case of a glass barrel formed from glass tubing. Further, the need to provide sufficient strength for the flange requires the proximal end of the barrel portion to be more massive than would be required to accommodate only the volume. This additional size may affect the ability of the syringe to be fit into syringe pumps.
In the case of syringes intended for prefilling and subsequent use as a package for a medicament, the presence of a fixed flange constrains the design of the processing and filling apparatus. Further, the presence of a fixed flange may make the barrel more prone to breakage during the processing and filling operations, as well as during handling, preparation and set up for the injection.
Syringes have been in use for many years. Several early designs of syringes have had flanges formed from materials other than glass and subsequently attached to the barrel by clamping, threading or the like. Patents exemplary of these types of devices are described below.
U.S. Pat. No. 801,912 teaches a glass syringe barrel with a proximal rim and a metal finger flange apparently put on from the distal end of the barrel and slid proximally to engage the rim. The metal flange is held against the rim by an internal flat spring compressed against the barrel.
U.S. Pat. No. 1,142,682 teaches a separate flange installed over the distal end of the syringe and slid proximally alonq the barrel to a proximal rim. The flange includes a spring which serves to hold the collar with the flange against the barrel's proximal rim and also maintains tension against the plunger.
U.S. Pat. No. 1,798,116 teaches a two part finger flange which has a threaded collar containing the flange placed over the distal end of the syringe, then slid upwardly to the proximal end of the syringe. A threaded plug is then inserted into the proximally placed threaded collar on top of a swedging ring and tightened down to hold the flange in position at the proximal end of the barrel.
U.S. Pat. No. 4,112,945 teaches a syringe designed to receive a prefilled cartridge which has threaded cap with radially extending arms to provide finger holds. When the cap is threaded onto the barrel containing the cartridge, the cap serves to retain the cartridge and provide the finger holds.
U.S. Pat. No. 4,469,482 teaches a disposable syringe having a finger grip connected around the barrel according to the "so-called snap-cap principle." This device apparently comprises a planar flange with a central extended collar to fit around and over the proximal end of the syringe. There is no teaching in the specification of the structure of the "so called snap cap," however, FIG. 1, element 16 apparently shows a semicircular projection on the cap in apparent conjugation with a recess on the proximal end of the barrel.
U.S. Pat. No. 4,702,329 teaches a syringe in which the cylindrical body is an ampoule having closures at each end. The proximal closure functions as a plunger stopper after attachment of a plunger rod. A finger grip is mounted on the outside of the ampoule by the "so-called snap cap principle." The '329 patent teaches that the finger grip is preferably manufactured from a slightly resilient but non-deformable material, for example a synthetic. The '329 patent also teaches another embodiment where the finger grip forms are one assembly with the ampoule and may then be formed as a flange like part of the ampoule projecting radially outwards.
British Patent Specification 1,479,536 teaches a finger grip consisting of a tensioning collet which is clamped around the end of the barrel by means of a tensioning sleeve. The patent teaches a finger grip preferably of slightly resilient material for example plastic.
While the art presented above shows several different forms of finger flanges made from metal, glass and plastic, most of the devices taught are multi-component, are applied from the distal end of the barrel and slid to the proximal side. In most of these prior art examples, the assembly of the finger flange requires a complex assembly procedure, a fitting on, a sliding together, a threading and a tightening. In some of the examples a hoop stress or compression is exerted upon the barrel by the flange assembly. Such a stress would be exacerbated by out of-roundness conditions which would tend to concentrate the stress. This stress may lead to distortion or cracking of the barrel, particularly when the barrel is glass.
Thus, in the field of syringes with finger flanges, there still exists a need for a simple to manufacture syringe assembly having as a design feature a finger flange with a higher force for removal than the force for assembly. The higher removal force provides functional utility while the lower installation force provides easy assembly.